Short Chain Fatty Acids and Fecal Microbiota Abundance in Humans with Obesity: A Systematic Review and Meta-Analysis

The short-chain fatty acid acetate modulates orexin/hypocretin neurons: A novel mechanism in gut-brain axis regulation of energy homeostasis and feeding

The short-chain fatty acids (SCFAs) acetate, propionate and butyrate, the major products of intestinal microbial fermentation of dietary fibres, are involved in fine-tuning brain functions via the gut-brain axis. However, the effects of SCFAs in the hypothalamic neuronal network regulating several autonomic-brain functions are still unknown. Using NMR spectroscopy, we detected a reduction in brain acetate concentrations in the hypothalamus of obese leptin knockout ob/ob mice compared to lean wild-type littermates. Therefore, we investigated the effect of acetate on orexin/hypocretin neurons (hereafter referred as OX or OX-A neurons), a subset of hypothalamic neurons regulating energy homeostasis, which we have characterized in previous studies to be over-activated by the lack of leptin and enhancement of endocannabinoid tone in the hypothalamus of ob/ob mice. We found that acetate reduces food-intake in concomitance with a reduction of orexin neuronal activity in ob/ob mice. This was demonstrated by evaluating food-intake behaviour and orexin-A/c-FOS immunoreactivity coupled with patch-clamp recordings in Hcrt-eGFP neurons, quantification of prepro-orexin mRNA, and immunolabeling of GPR-43, the main acetate receptor. Our data provide new insights into the mechanisms of the effects of chronic dietary supplementation with acetate, or complex carbohydrates, on energy intake and body weight, which may be partly mediated by inhibition of orexinergic neuron activity.

Changes in microbial diversity and volatile metabolites during the fermentation of Bulang pickled tea

The present study aimed to determine microbial community, short-chain fatty acids (SCFAs), and volatilome of Bulang pickled tea during fermentation. Sequencing of 16S rRNA and ITS revealed that Bualng pickled tea was dominated by Lactobacillus plantarum, unclassified Enterobacteriaceae, unclassified Debaryomyces, Candida metapsilosis, Cladosporium sphaerospermum, and unclassified Aspergillus. The overall contents of SCFAs increased, with acetic acid showing the highest content. A total of 398 differential volatile metabolites were detected using differential metabolomics analysis. Out of these different volatile compounds, ten key volatile compounds including (Z)-4-heptenal, 1-(2-thienyl)-ethanone, 5-methyl-(E)-2-hepten-4-one, 2-ethoxy-3-methylpyrazine, p-cresol, 2-methoxy-phenol, ethy-4-methylvalerate, 3-ethyl-phenol, p-menthene-8-thiol, and 2-s-butyl-3-methoxypyrazinewere were screened based on odor activity value (OAV). The Spearman correlation analysis showed a high correlation of SCFAs and volatile compounds with microorganisms, especially L. plantarum and C. sphaerospermum. This study provided a theoretical basis for elucidating the flavor quality formation mechanism of Bulang pickled tea.

Gut-liver axis: Potential mechanisms of action of food-derived extracellular vesicles

Food-derived extracellular vesicles (FEVs) are nanoscale membrane vesicles obtained from dietary materials such as breast milk, plants and probiotics. Distinct from other EVs, FEVs can survive the harsh degrading conditions in the gastrointestinal tract and reach the intestines. This unique feature allows FEVs to be promising prebiotics in health and oral nanomedicine for gut disorders, such as inflammatory bowel disease. Interestingly, therapeutic effects of FEVs have recently also been observed in non-gastrointestinal diseases. However, the mechanisms remain unclear or even mysterious. It is speculated that orally administered FEVs could enter the bloodstream, reach remote organs, and thus exert therapeutic effects therein. However, emerging evidence suggests that the amount of FEVs reaching organs beyond the gastrointestinal tract is marginal and may be insufficient to account for the significant therapeutic effects achieved regarding diseases involving remote organs such as the liver. Thus, we herein propose that FEVs primarily act locally in the intestine by modulating intestinal microenvironments such as barrier integrity and microbiota, thereby eliciting therapeutic impact remotely on the liver in non-gastrointestinal diseases via the gut-liver axis. Likewise, drugs delivered to the gastrointestinal system through FEVs may act via the gut-liver axis. As the liver is the main metabolic hub, the intestinal microenvironment may be implicated in other metabolic diseases. In fact, many patients with non-alcoholic fatty liver disease, obesity, diabetes and cardiovascular disease suffer from a leaky gut and dysbiosis. In this review, we provide an overview of the recent progress in FEVs and discuss their biomedical applications as therapeutic agents and drug delivery systems, highlighting the pivotal role of the gut-liver axis in the mechanisms of action of FEVs for the treatment of gut disorders and metabolic diseases.

Short-Chain Fatty Acids and Preeclampsia: A Scoping Review

BACKGROUND

Preeclampsia (PE) is a pregnancy-associated hypertension disorder with high morbidity and mortality. Short-chain fatty acids (SCFAs)-molecules produced by gut microbes-have been associated with hypertension, yet their relation to PE remains uncertain.

OBJECTIVES

The aim was to review existing human studies that examined associations of the major SCFAs (acetate, propionate, butyrate) in pregnancy with PE development.

METHODS

Two reviewers independently searched online databases (EMBASE, PubMed, Web of Science, and Cochrane Database of Systematic Reviews) in January 2024 using the following terms: "short-chain fatty acids," "acetic acid," "butyric acid," "propionic acid," and "preeclampsia." The final set of included studies had to report associations of SCFAs with PE, be peer-reviewed, be written in English, and be conducted in humans.

RESULTS

The abstracts of 907 studies were screened; 43 underwent full-text screening and 11 (1318 total participants, 352 with PE) were included in the final review. All studies used a case-control design. SCFAs were measured in a range of biospecimens (eg, serum, plasma, feces, placentas, and amniotic fluid) that were collected at distinct time points in pregnancy. All 7 studies that investigated butyrate found that it was lower in PE cases than in controls, with 6 of these showing statistical significance (P < .05). Five studies showed that acetate was significantly lower in individuals with PE compared with healthy individuals, while 1 study found that acetate was significantly higher in PE cases. One study reported significantly higher propionate among PE cases vs controls, while 2 studies reported significantly lower propionate levels in PE cases. The nuance in results for acetate and propionate may owe to reasons such as differences in distributions of population characteristics associated with SCFA level and PE or type of PE (early vs late).

CONCLUSION

Current epidemiologic evidence, which derives only from case-control studies, suggests that SCFAs, particularly butyrate (protective), in pregnancy are related to the development of PE. Large-cohort studies are warranted to investigate the temporality and potential causality of these associations.

Gut microbiota promoting propionic acid production accompanies caloric restriction-induced intentional weight loss in cats

Rodent models and human clinical studies have shown gut microbiota-derived short-chain fatty acids (SCFAs) play roles in obesity and insulin resistance. These roles have been minimally explored in cats, where in the USA an estimated 60% of cats are overweight or obese. Overweight/obese research cats (n = 7) were transitioned from a maintenance diet to a reduced calorie diet fed ad libitum for 7 days, then calories were restricted to achieve 1-2% weight loss per week for an additional 77 days. Cats then received their original maintenance diet again for 14 days. Significant intentional weight loss was noted after calorie restriction (adjusted p < 0.0001). 16S rRNA gene amplicon sequencing and targeted SCFA metabolomics were performed on fecal samples. Fecal microbial community structure significantly differed between the four study phases (PERMANOVA p = 0.011). Fecal propionic acid was significantly higher during caloric restriction-induced weight loss (adjusted p < 0.05). Repeated measures correlation revealed the relative abundances of Prevotella 9 copri (correlation coefficient = 0.532, 95% CI (0.275, 0.717), p = 0.0002) significantly correlated with propionic acid composition. Like humans, obese cats experienced an altered microbial community structure and function, favoring propionic acid production, during caloric restriction-induced weight loss.

Computational prediction of new therapeutic effects of probiotics

Probiotics are living microorganisms that provide health benefits to their hosts, potentially aiding in the treatment or prevention of various diseases, including diarrhea, irritable bowel syndrome, ulcerative colitis, and Crohn's disease. Motivated by successful applications of link prediction in medical and biological networks, we applied link prediction to the probiotic-disease network to identify unreported relations. Using data from the Probio database and International Classification of Diseases-10th Revision (ICD-10) resources, we constructed a bipartite graph focused on the relationship between probiotics and diseases. We applied customized link prediction algorithms for this bipartite network, including common neighbors, Jaccard coefficient, and Adamic/Adar ranking formulas. We evaluated the results using Area under the Curve (AUC) and precision metrics. Our analysis revealed that common neighbors outperformed the other methods, with an AUC of 0.96 and precision of 0.6, indicating that basic formulas can predict at least six out of ten probable relations correctly. To support our findings, we conducted an exact search of the top 20 predictions and found six confirming papers on Google Scholar and Science Direct. Evidence suggests that Lactobacillus jensenii may provide prophylactic and therapeutic benefits for gastrointestinal diseases and that Lactobacillus acidophilus may have potential activity against urologic and female genital illnesses. Further investigation of other predictions through additional preclinical and clinical studies is recommended. Future research may focus on deploying more powerful link prediction algorithms to achieve better and more accurate results.

Effects of dietary fibre on metabolic health and obesity

Obesity and metabolic syndrome represent a growing epidemic worldwide. Body weight is regulated through complex interactions between hormonal, neural and metabolic pathways and is influenced by numerous environmental factors. Imbalances between energy intake and expenditure can occur due to several factors, including alterations in eating behaviours, abnormal satiation and satiety, and low energy expenditure. The gut microbiota profoundly affects all aspects of energy homeostasis through diverse mechanisms involving effects on mucosal and systemic immune, hormonal and neural systems. The benefits of dietary fibre on metabolism and obesity have been demonstrated through mechanistic studies and clinical trials, but many questions remain as to how different fibres are best utilized in managing obesity. In this Review, we discuss the physiochemical properties of different fibres, current findings on how fibre and the gut microbiota interact to regulate body weight homeostasis, and knowledge gaps related to using dietary fibres as a complementary strategy. Precision medicine approaches that utilize baseline microbiota and clinical characteristics to predict individual responses to fibre supplementation represent a new paradigm with great potential to enhance weight management efficacy, but many challenges remain before these approaches can be fully implemented.

Butyrate as a promising therapeutic target in cancer: From pathogenesis to clinic (Review)

Cancer is one of the leading causes of mortality worldwide. The etiology of cancer has not been fully elucidated yet, and further enhancements are necessary to optimize therapeutic efficacy. Butyrate, a short‑chain fatty acid, is generated through gut microbial fermentation of dietary fiber. Studies have unveiled the relevance of butyrate in malignant neoplasms, and a comprehensive understanding of its role in cancer is imperative for realizing its full potential in oncological treatment. Its full antineoplastic effects via the activation of G protein‑coupled receptors and the inhibition of histone deacetylases have been also confirmed. However, the underlying mechanistic details remain unclear. The present study aimed to review the involvement of butyrate in carcinogenesis and its molecular mechanisms, with a particular emphasis on its association with the efficacy of tumor immunotherapy, as well as discussing relevant clinical studies on butyrate as a therapeutic target for neoplastic diseases to provide new insights into cancer treatment.

Inhalation of diesel exhaust particulate matter accelerates weight gain via regulation of hypothalamic appetite-related genes and gut microbiota metabolism

Mice exposed to diesel exhaust particulate matter (DEPM) exhibited accelerated weight gain. Several hypothalamic genes, hormones (serum Hypothalamic-Pituitary-Adrenal (HPA) axis hormones and gastrointestinal peptide tyrosine tyrosine (PYY)), metabolites (intrahepatic triglyceride (IHTG) and fecal short-chain fatty acids (SCFAs)), and gut microbiota structure, which may influence obesity and appetite regulation, were examined. The result suggested that DEPM-induced accelerated weight gain may be associated with increased expression of hypothalamic Gamma-aminobutyric acid (GABA) type B receptor, tight junction protein, and orexin receptors, in addition with decreased IHTG and repressed HPA axis. Moreover, changes in the structure of intestinal microbiota are also related to weight changes, especially for phylum Firmicutes, genus Lactobacillus, and the ratio of relative abundance of Firmicutes and Bacteroidetes (F/B). DEPM exposure also caused widespread increase in the levels of intestinal SCFAs, the concentrations of propionic acid and isobutyric acid were associated with weight gain rate and the abundance of some bacteria. Although DEPM exposure caused changes in expression of hypothalamic serotonin, NPY, and melanocortin receptors, they were not associated with weight changes. Furthermore, no significant difference in gastrointestinal PYY and expression of hypothalamic receptors for leptin, insulin, and glucagon-like peptide 1 receptors was observed between DEPM-exposed and control mice.

Effect of inulin on breath hydrogen, postprandial glycemia, gut hormone release, and appetite perception in RYGB patients: a prospective, randomized, cross-over pilot study

BACKGROUND AND OBJECTIVE

Large intestinal fermentation of dietary fiber may control meal-related glycemia and appetite via the production of short-chain fatty acids (SCFA) and the secretion of glucagon-like peptide-1 (GLP-1) and peptide YY (PYY). We investigated whether this mechanism contributes to the efficacy of the Roux-en-Y gastric bypass (RYGB) by assessing the effect of oligofructose-enriched inulin (inulin) vs. maltodextrin (MDX) on breath hydrogen (a marker of intestinal fermentation), plasma SCFAs, gut hormones, insulin and blood glucose concentrations as well as appetite in RYGB patients.

METHOD

Eight RYGB patients were studied on two occasions before and ~8 months after surgery using a cross-over design. Each patient received 300 ml orange juice containing 25 g inulin or an equicaloric load of 15.5 g MDX after an overnight fast followed by a fixed portion snack served 3 h postprandially. Blood samples were collected over 5 h and breath hydrogen measured as well as appetite assessed using visual analog scales.

RESULTS

Surgery increased postprandial secretion of GLP-1 and PYY (P ≤ 0.05); lowered blood glucose and plasma insulin increments (P ≤ 0.05) and reduced appetite ratings in response to both inulin and MDX. The effect of inulin on breath hydrogen was accelerated after surgery with an increase that was earlier in onset (2.5 h vs. 3 h, P ≤ 0.05), but less pronounced in magnitude. There was, however, no effect of inulin on plasma SCFAs or plasma GLP-1 and PYY after the snack at 3 h, neither before nor after surgery. Interestingly, inulin appeared to further potentiate the early-phase glucose-lowering and second-meal (3-5 h) appetite-suppressive effect of surgery with the latter showing a strong correlation with early-phase breath hydrogen concentrations.

CONCLUSION

RYGB surgery accelerates large intestinal fermentation of inulin, however, without measurable effects on plasma SCFAs or plasma GLP-1 and PYY. The glucose-lowering and appetite-suppressive effects of surgery appear to be potentiated with inulin.

Dissecting mechanisms of fecal microbiota transplantation efficacy in disease

Fecal microbiota transplantation (FMT) has emerged as an alternative or adjunct experimental therapy for microbiome-associated diseases following its success in the treatment of recurrent Clostridioides difficile infections (rCDIs). However, the mechanisms of action involved remain relatively unknown. The term 'dysbiosis' has been used to describe microbial imbalances in relation to disease, but this traditional definition fails to consider the complex cross-feeding networks that define the stability of the microbiome. Emerging research transitions toward the targeted restoration of microbial functional networks in treating different diseases. In this review, we explore potential mechanisms responsible for the efficacy of FMT and future therapeutic applications, while revisiting definitions of 'dysbiosis' in favor of functional network restoration in rCDI, inflammatory bowel diseases (IBDs), metabolic diseases, and cancer.

Sex differences in the association between dual-energy x-ray absorptiometry-measured body composition and periodontitis

BACKGROUND

A positive association between obesity based on body mass index (BMI) and periodontitis has been reported. Fat tissue-related systemic inflammation acts as the link to periodontal comorbidities of obesity. However, the BMI is unable to distinguish fat and fat-free tissues. More precise measures are required to evaluate body composition, including fat and fat-free tissues. This study aimed to determine the sex differences in the association between dual-energy x-ray absorptiometry (DXA)-measured body composition (i.e., fat mass and muscle mass) and phenotypes with periodontitis.

METHODS

Cross-sectional data of 3892 participants from the National Health and Nutrition Examination Survey (NHANES) study 2011‒2014 were analyzed. Adiposity indices (fat mass index [FMI] and percentage body fat [%BF]) and muscle mass index (MMI) were calculated. The participants were categorized by the quintiles of FMI, MMI, and %BF. Body composition phenotypes were categorized as: low adiposity-low muscle (LA-LM), low adiposity-high muscle (LA-HM), high adiposity-low muscle (HA-LM), or high adiposity-high muscle (HA-HM), respectively. Periodontitis was defined by the CDC/AAP (Centers for Disease Control and Prevention/American Academy of Periodontology) criteria. Multivariable logistic regression analysis was conducted, stratified by sex. We further adjusted for white blood cell (WBC) counts in the sensitivity analysis.

RESULTS

Restricted cubic splines revealed non-linear associations between body composition indices and periodontitis risk. Women with a higher FMI (odds ratio for Q5 vs. Q1 [ORQ5vs1] = 1.787, 95% confidence interval: 1.209-2.640) or %BF (ORQ5vs1 = 2.221, 1.509-3.268) had increased odds of periodontitis. In addition, women with HA-LM phenotype were more likely to develop periodontitis (OR = 1.528, 1.037-2.252). Interestingly, the WBC count, a systemic inflammatory biomarker, attenuated these associations. No statistically significant associations were found in men.

CONCLUSIONS

The association between DXA-measured body composition and phenotypes with periodontitis differs per sex. Only in women higher adiposity indices and HA-LM phenotype were associated with an increased risk of periodontitis.

Anti-obesity effects of mulberry leaf extracts on female high-fat diet-induced obesity: Modulation of white adipose tissue, gut microbiota, and metabolic markers

Mulberry leaves (MLs) are reported to have beneficial effects in modulating obesity in male models. However, the impact of different types of mulberry leaf extracts (MLEs) on female models, specifically their influence on adipocytes, gut microbiota, and related metabolic markers, remains poorly understood. In this study, we observed a strong correlation between the total phenolic content (TPC), antioxidant and adipocyte modulation effects of water extracted MLEs. HB-W (water-extracted baiyuwang) and HY-W (water-extracted Yueshen) demonstrated remarkable inhibition effects on adipocytes in 3 T3-L1 adipocytes model. Moreover, MLEs effectively reduced the levels of triglycerides (TG), non-esterified fatty acids (NEFA), and total cholesterol (T-CHO) in adipocytes in vitro. In vivo experiments conducted on female mice with high fat diet (HFD)-induced obesity revealed the anti-obesity effects of HB-W and HY-W, leading to a significant decrease in weight gain rates and notable influence on the ratios of adipose tissue, particularly white adipose tissue (WAT). Gene expression analysis demonstrated the up-regulation of WAT-related genes (Pla2g2a and Plac8) by HB-W, while HY-W supplementation showed beneficial effects on the regulation of blood sugar-related genes. Furthermore, both HB-W and HY-W exhibited modulatory effects on obesity-related gut microbiota (Firmicutes-to-Bacteroidetes ratio) and short chain fatty acid (SCFA) contents. Importantly, they also mitigated abnormalities in liver function and uncoupling protein 1 (UPC1) expression. Overall, our findings underscore the anti-obesity effects of MLEs in female rats with high-fat diet-induced obesity.

Biomarkers of Metabolic Adaptation to High Dietary Fats in a Mouse Model of Obesity Resistance

Obesity-resistant (non-responder, NR) phenotypes that exhibit reduced susceptibility to developing obesity despite being exposed to high dietary fat are crucial in exploring the metabolic responses that protect against obesity. Although several efforts have been made to study them in mice and humans, the individual protective mechanisms are poorly understood. In this exploratory study, we used a polygenic C57BL/6J mouse model of diet-induced obesity to show that NR mice developed healthier fat/lean body mass ratios (0.43 ± 0.05) versus the obesity-prone (super-responder, SR) phenotypes (0.69 ± 0.07, p < 0.0001) by upregulating gene expression networks that promote the accumulation of type 2a, fast-twitch, oxidative muscle tissues. This was achieved in part by a metabolic adaptation in the form of blood glucose sparing, thus aggravating glucose tolerance. Resistance to obesity in NR mice was associated with 4.9-fold upregulated mitoferrin 1 (Slc25a37), an essential mitochondrial iron importer. SR mice also showed fecal volatile metabolite signatures of enhanced short-chain fatty acid metabolism, including increases in detrimental methyl formate and ethyl propionate, and these effects were reversed in NR mice. Continued research into obesity-resistant phenotypes can offer valuable insights into the underlying mechanisms of obesity and metabolic health, potentially leading to more personalized and effective approaches for managing weight and related health issues.

Probiotic-Induced Modulation of Microbiota Composition and Antibiotic Resistance Genes Load, an In Vitro Assessment

The imbalance of the gut microbiota (GM) is known as dysbiosis and is associated with disorders such as obesity. The increasing prevalence of microorganisms harboring antibiotic resistance genes (ARG) in the GM has been reported as a potential risk for spreading multi-drug-resistant pathogens. The objective of this work was the evaluation, in a fecal culture model, of different probiotics for their ability to modulate GM composition and ARG levels on two population groups, extremely obese (OB) and normal-weight (NW) subjects. Clear differences in the basal microbiota composition were observed between NW and OB donors. The microbial profile assessed by metataxonomics revealed the broader impact of probiotics on the OB microbiota composition. Also, supplementation with probiotics promoted significant reductions in the absolute levels of tetM and tetO genes. Regarding the blaTEM gene, a minor but significant decrease in both donor groups was detected after probiotic addition. A negative association between the abundance of Bifidobacteriaceae and the tetM gene was observed. Our results show the ability of some of the tested strains to modulate GM. Moreover, the results suggest the potential application of probiotics for reducing the levels of ARG, which constitutes an interesting target for the future development of probiotics.

Bacteroides methylmalonyl-CoA mutase produces propionate that promotes intestinal goblet cell differentiation and homeostasis

Propionate is a short-chain fatty acid that is generated upon microbiome-mediated fiber fermentation in the intestine. By modulating immune and metabolic pathways, propionate exerts many health benefits. Key bacterial species, such as Bacteroides thetaiotaomicron, generate propionate, but the biochemical pathways and specific functions remain undetermined. We identified a gene operon-encoding methylmalonyl-CoA mutase (MCM) that contributes to propionate biosynthesis in B. thetaiotaomicron. Colonization of germ-free mice with wild-type or MCM-deficient strains as well as in vitro examination demonstrated that MCM-mediated propionate production promotes goblet cell differentiation and mucus-related gene expression. Intestinal organoids lacking the propionate receptor, GPR41, showed reduced goblet cell differentiation upon MCM-mediated propionate production. Furthermore, although wild-type B. thetaiotaomicron alleviated DSS-induced intestinal inflammation, this effect was abolished in mice receiving the MCM-deficient strain but restored upon propionate supplementation. These data emphasize the critical role of MCM-mediated propionate biosynthesis in goblet cell differentiation, offering potential pathways to ameliorate colitis.

Short-chain fatty acids and insulin sensitivity: a systematic review and meta-analysis

CONTEXT

There is substantial evidence that reduced short-chain fatty acids (SCFAs) in the gut are associated with obesity and type 2 diabetes, although findings from clinical interventions that can increase SCFAs are inconsistent.

OBJECTIVE

This systematic review and meta-analysis aimed to assess the effect of SCFA interventions on fasting glucose, fasting insulin, and homeostatic model assessment of insulin resistance (HOMA-IR).

DATA SOURCES

Relevant articles published up to July 28, 2022, were extracted from PubMed and Embase using the MeSH (Medical Subject Headings) terms of the defined keywords [(short-chain fatty acids) AND (obesity OR diabetes OR insulin sensitivity)] and their synonyms. Data analyses were performed independently by two researchers who used the Cochrane meta-analysis checklist and the PRISMA guidelines.

DATA EXTRACTION

Clinical studies and trials that measured SCFAs and reported glucose homeostasis parameters were included in the analysis. Standardized mean differences (SMDs) with 95%CIs were calculated using a random-effects model in the data extraction tool Review Manager version 5.4 (RevMan 5.4). The risk-of-bias assessment was performed following the Cochrane checklist for randomized and crossover studies.

DATA ANALYSIS

In total, 6040 nonduplicate studies were identified, 23 of which met the defined criteria, reported fasting insulin, fasting glucose, or HOMA-IR values, and reported change in SCFA concentrations post intervention. Meta-analyses of these studies indicated that fasting insulin concentrations were significantly reduced (overall effect: SMD = -0.15; 95%CI = -0.29 to -0.01, P = 0.04) in treatment groups, relative to placebo groups, at the end of the intervention. Studies with a confirmed increase in SCFAs at the end of intervention also had a significant effect on lowering fasting insulin (P = 0.008). Elevated levels of SCFAs, compared with baseline levels, were associated with beneficial effects on HOMA-IR (P < 0.00001). There was no significant change in fasting glucose concentrations.

CONCLUSION

Increased postintervention levels of SCFAs are associated with lower fasting insulin concentrations, offering a beneficial effect on insulin sensitivity.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration number CRD42021257248.

Gut microbes in metabolic disturbances. Promising role for therapeutic manipulations?

The prevalence of overweight, obesity, type 2 diabetes, metabolic syndrome and steatotic liver disease is rapidly increasing worldwide with a huge economic burden in terms of morbidity and mortality. Several genetic and environmental factors are involved in the onset and development of metabolic disorders and related complications. A critical role also exists for the gut microbiota, a complex polymicrobial ecology at the interface of the internal and external environment. The gut microbiota contributes to food digestion and transformation, caloric intake, and immune response of the host, keeping the homeostatic control in health. Mechanisms of disease include enhanced energy extraction from the non-digestible dietary carbohydrates, increased gut permeability and translocation of bacterial metabolites which activate a chronic low-grade systemic inflammation and insulin resistance, as precursors of tangible metabolic disorders involving glucose and lipid homeostasis. The ultimate causative role of gut microbiota in this respect remains to be elucidated, as well as the therapeutic value of manipulating the gut microbiota by diet, pre- and pro- synbiotics, or fecal microbial transplantation.

Inflammatory Pathways in Overweight and Obese Persons as a Potential Mechanism for Cognitive Impairment and Earlier Onset Alzeihmer's Dementia in the General Population: A Narrative Review

The overweight status or obesity can be confirmed through classical methods such as the body mass index (BMI) and the waist-to-hip ratio (WHR). Apart from metabolic issues such as atherosclerosis, liver steatosis, or diabetes mellitus, long-term obesity or overweight status can pose a risk for cardiovascular and neurovascular complications. While some acute adverse events like coronary syndromes of strokes are well-documented to be linked to an increased body mass, there are also chronic processes that, due to their silent onset and evolution, are underdiagnosed and not as thoroughly studied. Through this review, we aimed to collect all relevant data with regard to the long-term impact of obesity on cognitive function in all ages and its correlation with an earlier onset of dementia such as Alzheimer's disease (AD). The exact mechanisms through which a decline in cognitive functions occurs in overweight or obese persons are still being discussed. A combination of factors has been acknowledged as potential triggers, such as a sedentary lifestyle and stress, as well as a genetic predisposition, for example, the apolipoprotein E (ApoE) alleles in AD. Most research highlights the impact of vascular dysfunction and systemic inflammation on the nervous system in patients with obesity and the subsequent neurological changes. Obesity during the early to mid-ages leads to an earlier onset of cognitive dysfunction in various forms. Also, lifestyle intervention can reverse cognitive dysfunction, especially dieting, to encourage weight loss.

Obesity is the main driver of altered gut microbiome functions in the metabolically unhealthy

Obesity (OB) and cardiometabolic disease are major public health issues linked to changes in the gut microbiome. OB and poor cardiometabolic health status (CHS) are often comorbid, which hinders efforts to identify components of the microbiome uniquely linked to either one. Here, we used a deeply phenotyped cohort of 408 adults from Colombia, including subjects with OB, unhealthy CHS, or both, to validate previously reported features of gut microbiome function and diversity independently correlated with OB or CHS using fecal metagenomes. OB was defined by body mass index, waist circumference, and body fat; CHS as healthy or unhealthy according to blood biochemistry and anthropometric data. We found that OB, more so than metabolic status, drove associations with gut microbiome structure and functions. The microbiome of obese individuals with and without co-existing unhealthy CHS was characterized by reduced metagenomic diversity, reduced fermentative potential and elevated capacity to respond to oxidative stress and produce bacterial antigens. Disease-linked features were correlated with increased host blood pressure and inflammatory markers, and were mainly contributed by members of the family Enterobacteriaceae. Our results link OB with a microbiome able to tolerate an inflammatory and oxygenated gut state, and suggest that OB is the main driver of microbiome functional differences when poor CHS is a comorbidity.

Adipokines and Bacterial Metabolites: A Pivotal Molecular Bridge Linking Obesity and Gut Microbiota Dysbiosis to Target

Adipokines are essential mediators produced by adipose tissue and exert multiple biological functions. In particular, adiponectin, leptin, resistin, IL-6, MCP-1 and PAI-1 play specific roles in the crosstalk between adipose tissue and other organs involved in metabolic, immune and vascular health. During obesity, adipokine imbalance occurs and leads to a low-grade pro-inflammatory status, promoting insulin resistance-related diabetes and its vascular complications. A causal link between obesity and gut microbiota dysbiosis has been demonstrated. The deregulation of gut bacteria communities characterizing this dysbiosis influences the synthesis of bacterial substances including lipopolysaccharides and specific metabolites, generated via the degradation of dietary components, such as short-chain fatty acids, trimethylamine metabolized into trimethylamine-oxide in the liver and indole derivatives. Emerging evidence suggests that these bacterial metabolites modulate signaling pathways involved in adipokine production and action. This review summarizes the current knowledge about the molecular links between gut bacteria-derived metabolites and adipokine imbalance in obesity, and emphasizes their roles in key pathological mechanisms related to oxidative stress, inflammation, insulin resistance and vascular disorder. Given this interaction between adipokines and bacterial metabolites, the review highlights their relevance (i) as complementary clinical biomarkers to better explore the metabolic, inflammatory and vascular complications during obesity and gut microbiota dysbiosis, and (ii) as targets for new antioxidant, anti-inflammatory and prebiotic triple action strategies.

Bariatric Surgery and Gut-Brain-Axis Driven Alterations in Cognition and Inflammation

Obesity is associated with systemic inflammation, comorbidities like diabetes, cardiovascular disease and several cancers, cognitive decline and structural and functional brain changes. To treat, or potentially prevent these related comorbidities, individuals with obesity must achieve long-term sustainable weight loss. Often life style interventions, such as dieting and increased physical activity are not successful in achieving long-term weight loss. Meanwhile bariatric surgery has emerged as a safe and effective procedure to treat obesity. Bariatric surgery causes changes in physiological processes, but it is still not fully understood which exact mechanisms are involved. The successful weight loss after bariatric surgery might depend on changes in various energy regulating hormones, such as ghrelin, glucagon-like peptide-1 and peptide YY. Moreover, changes in microbiota composition and white adipose tissue functionality might play a role. Here, we review the effect of obesity on neuroendocrine effects, microbiota composition and adipose tissue and how these may affect inflammation, brain structure and cognition. Finally, we will discuss how these obesity-related changes may improve after bariatric surgery.

The Bern Birth Cohort (BeBiCo) to study the development of the infant intestinal microbiota in a high-resource setting in Switzerland: rationale, design, and methods

BACKGROUND

Microbiota composition is fundamental to human health with the intestinal microbiota undergoing critical changes within the first two years of life. The developing intestinal microbiota is shaped by maternal seeding, breast milk and its complex constituents, other nutrients, and the environment. Understanding microbiota-dependent pathologies requires a profound understanding of the early development of the healthy infant microbiota.

METHODS

Two hundred and fifty healthy pregnant women (≥20 weeks of gestation) from the greater Bern area will be enrolled at Bern University hospital's maternity department. Participants will be followed as mother-baby pairs at delivery, week(s) 1, 2, 6, 10, 14, 24, 36, 48, 96, and at years 5 and 10 after birth. Clinical parameters describing infant growth and development, morbidity, and allergic conditions as well as socio-economic, nutritional, and epidemiological data will be documented. Neuro-developmental outcomes and behavior will be assessed by child behavior checklists at and beyond 2 years of age. Maternal stool, milk, skin and vaginal swabs, infant stool, and skin swabs will be collected at enrolment and at follow-up visits. For the primary outcome, the trajectory of the infant intestinal microbiota will be characterized by 16S and metagenomic sequencing regarding composition, metabolic potential, and stability during the first 2 years of life. Secondary outcomes will assess the cellular and chemical composition of maternal milk, the impact of nutrition and environment on microbiota development, the maternal microbiome transfer at vaginal or caesarean birth and thereafter on the infant, and correlate parameters of microbiota and maternal milk on infant growth, development, health, and mental well-being.

DISCUSSION

The Bern birth cohort study will provide a detailed description and normal ranges of the trajectory of microbiota maturation in a high-resource setting. These data will be compared to data from low-resource settings such as from the Zimbabwe-College of Health-Sciences-Birth-Cohort study. Prospective bio-sampling and data collection will allow studying the association of the microbiota with common childhood conditions concerning allergies, obesity, neuro-developmental outcomes , and behaviour. Trial registration The trial has been registered at www.

CLINICALTRIALS

gov , Identifier: NCT04447742.

Gut commensals and their metabolites in health and disease

Purpose of review

This review comprehensively discusses the role of the gut microbiome and its metabolites in health and disease and sheds light on the importance of a holistic approach in assessing the gut.

Recent findings

The gut microbiome consisting of the bacteriome, mycobiome, archaeome, and virome has a profound effect on human health. Gut dysbiosis which is characterized by perturbations in the microbial population not only results in gastrointestinal (GI) symptoms or conditions but can also give rise to extra-GI manifestations. Gut microorganisms also produce metabolites (short-chain fatty acids, trimethylamine, hydrogen sulfide, methane, and so on) that are important for several interkingdom microbial interactions and functions. They also participate in various host metabolic processes. An alteration in the microbial species can affect their respective metabolite concentrations which can have serious health implications. Effective assessment of the gut microbiome and its metabolites is crucial as it can provide insights into one's overall health.

Summary

Emerging evidence highlights the role of the gut microbiome and its metabolites in health and disease. As it is implicated in GI as well as extra-GI symptoms, the gut microbiome plays a crucial role in the overall well-being of the host. Effective assessment of the gut microbiome may provide insights into one's health status leading to more holistic care.

Emissions and mitigation potential of endocrine disruptors during outdoor exercise: Fate, transport, and implications for human health

The endocrine system is responsible for secreting and controlling hormones crucial in regulating key body activities. However, endocrine disruptors or endocrine-disrupting chemicals (EDCs) can harm human health and well-being by interfering with this complex process. This report seeks to assess the present state of understanding about endocrine disruptors in China, including their origins, impacts, and obstacles, and to provide actionable recommendations for reducing exposure and mitigating negative effects. Strong negative correlations between ANOE and rural ecological compensation (REC) and a negative correlation between ANOE and forest coverage (FC) were found in this analysis of the relationships between agricultural nitrous oxide emissions (ANOE), agricultural methane emissions (AME), and land use and land cover variables (LUPC). Just as LUPC is significantly inversely related to FC, AME is positively related. The team uses a gradient-boosted model (GBM) with a Gaussian loss function and fine-tunes the model's parameters to achieve optimal performance and reliable prediction results. With a relative relevance score of 90.36 for ANOE and 67.64 for AME, the analysis shows that LUPC is the most important factor in influencing emission levels. This study aims to increase knowledge of endocrine disruptors' potential advantages and disadvantages in outdoor exercise. The study aims to aid in preventing and managing many diseases and disorders caused by hormonal imbalances or disruptions by examining the origins, effects, and potential mitigation of these substances during outdoor activity. Safe and healthful outdoor exercise is promoted by the study's efforts to discover and implement effective and sustainable solutions to decrease emissions and exposure to endocrine disruptors. This comprehensive study aims to promote a healthier and more sustainable environment for individuals engaging in outdoor exercise by synthesizing current knowledge, providing practical recommendations, and emphasizing the importance of awareness and action.

The relationship between gut microbiota, short-chain fatty acids, and glucolipid metabolism in pregnant women with large for gestational age infants

AIM

To elucidate the association between gut microbiota, short-chain fatty acids (SCFAs), and glucolipid metabolism in women with large for gestational age (LGA) infants.

METHODS AND RESULTS

A single-center, observational prospective cohort study was performed at a tertiary hospital in Wenzhou, China. Normal pregnant women were divided into LGA group and appropriate for gestational age (AGA) group according to the neonatal birth weight. Fecal samples were collected from each subject before delivery for the analysis of gut microbiota composition (GMC) and SCFAs. Blood samples were obtained at 24-28 weeks of gestation age to measure fasting blood glucose and fasting insulin levels, as well as just before delivery to assess serum triglycerides, total cholesterol, high-density lipoprotein (HDL), and low-density lipoprotein. The GMC exhibited differences at various taxonomic levels. Within the Firmicutes phylum, genus Lactobacillus, genus Clostridium, species Lactobacillus agil, and species Lactobacillus salivarius were enriched in the LGA group. Microbispora at genus level, Microbispora rosea at species level belonging to the Actinobacteria phylum, Neisseriales at order level, Bartonellaceae at family level, Paracoccus aminovorans, and Methylobacterium at genus level from the Proteobacteria phylum were more abundant in the LGA group. In contrast, within the Bacteroidetes phylum, Prevotella at genus level and Parabacteroides distasonis at species level were enriched in the AGA group. Although there were few differences observed in SCFA levels and most glucolipid metabolism indicators between the two groups, the serum HDL level was significantly lower in the LGA group compared to the AGA group. No significant relevance among GMC, SCFAs, and glucolipid metabolism indicators was found in the LGA group or in the AGA group.

CONCLUSIONS

Multiple different taxa, especially phylum Firmicutes, genus Prevotella, and genus Clostridium, might play an important role in excessive fetal growth, and LGA might be associated with the lower serum HDL level.

Dietary fiber deficiency in individuals with metabolic syndrome: a review

PURPOSE OF REVIEW

Metabolic syndrome (MetS) refers to a group of risk factors, which increase the risk of cardiovascular disease (CVD), type 2 diabetes (T2D), and other chronic diseases. Dietary fiber has been shown to mitigate many of the effects of various risk factors associated with MetS. Our review summarizes the recent findings on the association between dietary fiber deficiency and MetS.

RECENT FINDINGS

A number of studies have shown that dietary fiber deficiency is associated with an increased risk of MetS. The main mechanisms by which dietary fiber may reduce the risk of MetS include reduction of cholesterol levels; improvement of blood sugar control; reduction of inflammation; and promotion of weight loss.

SUMMARY

Literature suggests that a deficiency in dietary fiber consumption is a risk factor for MetS. An increase in dietary fiber intake may help to reduce the risk of developing MetS and its associated chronic diseases.

Low Short-Chain-Fatty-Acid-Producing Activity of the Gut Microbiota Is Associated with Hypercholesterolemia and Liver Fibrosis in Patients with Metabolic-Associated (Non-Alcoholic) Fatty Liver Disease

The aim of this study was to investigate the short-chain fatty acid (SCFA) activity of the gut microbiota of patients with metabolic-associated fatty liver disease (MAFLD). The level and spectrum of short-chain fatty acids (SCFAs) were determined via gas–liquid chromatography. Liver fibrosis was assessed using the FIB-4 index and elastography. Among 42 non-cirrhotic MAFLD patients, 24 had high fecal SCFA levels (group H) and 18 had low fecal SCFA levels (group L). Patients in group H had lower serum uric acid, total cholesterol, and LDL cholesterol levels but a higher BMI than those in group L. All patients in group L and only 37.9% of those in group H were found to have hypercholesterolemia. In patients with hypercholesterolemia, the level of SCFAs was lower than that in patients without hypercholesterolemia. Patients in group H had less liver fibrosis than patients in group L. A total of 50.0% of the patients in group H and 92.3% of those in group L had significant liver fibrosis (≥F2). Patients with significant liver fibrosis had lower levels of fecal SCFAs—particularly acetate and butyrate. The fecal SCFA levels were positively correlated with gamma-glutamyl transferase, total bilirubin levels, BMI, and platelet count and were negatively correlated with FIB-4, liver stiffness, serum total, and LDL cholesterol levels.

The Influence of Probiotic Supplementation on the Obesity Indexes, Neuroinflammatory and Oxidative Stress Markers, Gut Microbial Diversity, and Working Memory in Obese Thai Children

Obesity is a worldwide health problem with a complex interaction between gut microbiota and cognition. Several studies have demonstrated that probiotic treatments improve characteristics linked to obesity. The present study aimed to evaluate the effects of probiotic supplementation on the obesity indexes, inflammatory and oxidative stress markers, gut microbiota, and working memory in obese children. Ten obese children were assigned to receive the probiotics (8 × 109 CFU of Lactobacillus paracasei HII01 and Bifidobacterium animalis subsp. lactis) for 12 weeks. Demographic data were recorded. Urine and fecal samples were collected to evaluate biomarkers related to obesity and cognition. Behavioral working memory was assessed using the visual n-back test. Electroencephalography was employed to measure electrical activity during the visual n-back test. All parameters were evaluated at the baseline and after 12 weeks. The results revealed that probiotic supplementation significantly altered some gut microbial metabolites, gut microbiota, total antioxidant capacity, and neuroinflammatory markers. However, no significant changes were observed in the visual n-back test or electroencephalographic recordings after 12 weeks. In conclusion, the use of probiotics might be an alternative treatment that could improve the gut microbial ecosystem and microbial metabolites, as well as host antioxidant and neuroinflammation levels. The preliminary results indicated that further detailed prolonged studies are needed in order to determine the beneficial effects of the studied probiotics.

Short chain fatty acids facilitate protective immunity by macrophages and T cells during acute fowl adenovirus-4 infection

Short chain fatty acids (SCFAs) are major gut metabolites that are involved in the regulation of dysfunction in immune responses, such as autoimmunity and cytokine storm. Numerous studies have reported a protective action of SCFAs against infectious diseases. This study investigated whether SCFAs have protective effect for immunity during fowl adenovirus-4 (FAdV-4) infection. We examined whether SCFA mixture (acetate, propionate, and butyrate) administration could protect against intramuscular challenge of a virulent viral strain. SCFA treatment promoted MHCII-expressing monocytes, the active form of T cells, and effector molecules in both peripheral and lymphoid tissues. It also boosted the production of immune molecules involved in pathogen elimination by intraepithelial lymphocytes and changed the intestinal microbial composition. We suggest that gut metabolites influence the gut microbial environment, and these changes stimulate macrophages and T cells to fight against the intramuscular challenge of FAdV-4.

The Complicated Relationship of Short-Chain Fatty Acids and Oral Microbiome: A Narrative Review

The human oral microbiome has emerged as a focal point of research due to its profound implications for human health. The involvement of short-chain fatty acids in oral microbiome composition, oral health, and chronic inflammation is gaining increasing attention. In this narrative review, the results of early in vitro, in vivo, and pilot clinical studies and research projects are presented in order to define the boundaries of this new complicated issue. According to the results, the current research data are disputable and ambiguous. When investigating the role of SCFAs in human health and disease, it is crucial to distinguish between their local GI effects and the systemic influences. Locally, SCFAs are a part of normal oral microbiota metabolism, but the increased formation of SCFAs usually attribute to dysbiosis; excess SCFAs participate in the development of local oral diseases and in oral biota gut colonization and dysbiosis. On the other hand, a number of studies have established the positive impact of SCFAs on human health as a whole, including the reduction of chronic systemic inflammation, improvement of metabolic processes, and decrease of some types of cancer incidence. Thus, a complex and sophisticated approach with consideration of origin and localization for SCFA function assessment is demanded. Therefore, more research, especially clinical research, is needed to investigate the complicated relationship of SCFAs with health and disease and their potential role in prevention and treatment.

Impact of intestinal microenvironments in obesity and bariatric surgery on shaping macrophages

Obesity is associated with alterations in tissue composition, systemic cellular metabolism, and low-grade chronic inflammation. Macrophages are heterogenous innate immune cells ubiquitously localized throughout the body and are key components of tissue homeostasis, inflammation, wound healing, and various disease states. Macrophages are highly plastic and can switch their phenotypic polarization and change function in response to their local environments. Here, we discuss how obesity alters the intestinal microenvironment and potential key factors that can influence intestinal macrophages as well as macrophages in other organs, including adipose tissue and hematopoietic organs. As bariatric surgery can induce metabolic adaptation systemically, we discuss the potential mechanisms through which bariatric surgery reshapes macrophages in obesity.

Multispecies probiotic affects fecal short-chain fatty acids in postmenopausal women with obesity: A post hoc analysis of a randomized, double-blind, placebo-controlled study

OBJECTIVES

Probiotics are known to regulate host metabolism. The aim of this study was to assess whether interventions with a multi-strain probiotic formula affect fecal short-chain fatty acids (SCFAs).

METHODS

The analysis was carried out in 56 obese, postmenopausal women randomized to three groups: probiotic dose 2.5 × 109 CFU/d (n = 18; lower probiotic dose [LPD]), 1 × 1010 CFU/d (n = 18; higher probiotic dose [HPD]), or placebo (n = 20).

RESULTS

An increase in three SCFA fecal concentrations in the HPD group was observed: acetic acid (C2; effect [E] = 1.72, SE = 0.73; 95% confidence interval [CI], 0.28-3.16; P = 0.019), butyric acid (C4; E = 0.98, SE = 0.46; 95% CI, 0.08-1.88; P = 0.033), and valeric acid (C5; E = 0.68, SE = 0.23; 95% CI, 0.23-1.12; P = 0.003). The mediation analysis showed that the decrease in uric acid under HPD may be transmitted through the elevation of C5 content. Multi-strain probiotic increases the SCFA content in the stool in a dose-dependent manner, which may diminish some cardiovascular risk factors because of a reduction in blood uric acid levels.

CONCLUSION

Assessing long-term health benefits requires further research, including assessment of blood SCFA concentrations and multiomic and mechanistic approaches.

Experimental Capacity of Human Fecal Microbiota to Degrade Fiber and Produce Short-Chain Fatty Acids Is Associated with Diet Quality and Anthropometric Parameters

BACKGROUND

Short-chain fatty acids (SCFAs) are considered beneficial to human health. The associations between bacterial capacity to produce SCFAs, diet, and health are not fully understood.

OBJECTIVE

We aimed to evaluate the capacity of human fecal microbiota to produce SCFAs and to metabolize soluble and insoluble fiber and to study its associations with human diet, anthropometric parameters, and carbohydrate and lipid metabolism.

METHODS

A cross-sectional study was carried out with 200 adult participants. Diet was evaluated using food records. Capacity to produce acetate, butyrate, and propionate and to degrade soluble fiber were assessed in an ex vivo experiment where fecal samples were inoculated in a pectin-containing broth. Fecal β-glucosidase activity was measured to assess potential to degrade insoluble fiber.

RESULTS

The main dietary determinants of high capacity to metabolize fiber were high intake of vegetables, fruits, nuts, and seeds. After adjusting analyses for confounders, glucose and lipid parameters were not significantly associated with any of the studied microbial capacities, but the capacity to produce propionic acid was significantly associated with hip circumference (β = -0.018, P = 0.044), which was seen especially in people eating healthy.

CONCLUSIONS

We confirmed that high intake of fiber-rich products is positively associated with the capacity of fecal microbiota to degrade soluble and insoluble dietary fiber and that people eating healthy food might benefit from enhanced microbial capacity to produce propionic acid.

The First 1000 Days of Life: How Changes in the Microbiota Can Influence Food Allergy Onset in Children

BACKGROUND

Allergic disease, including food allergies (FA)s, has been identified as a major global disease. The first 1000 days of life can be a "window of opportunity" or a "window of susceptibility", during which several factors can predispose children to FA development. Changes in the composition of the gut microbiota from pregnancy to infancy may play a pivotal role in this regard: some bacterial genera, such as Lactobacillus and Bifidobacterium, seem to be protective against FA development. On the contrary, Clostridium and Staphylococcus appear to be unprotective.

METHODS

We conducted research on the most recent literature (2013-2023) using the PubMed and Scopus databases. We included original papers, clinical trials, meta-analyses, and reviews in English. Case reports, series, and letters were excluded.

RESULTS

During pregnancy, the maternal diet can play a fundamental role in influencing the gut microbiota composition of newborns. After birth, human milk can promote the development of protective microbial species via human milk oligosaccharides (HMOs), which play a prebiotic role. Moreover, complementary feeding can modify the gut microbiota's composition.

CONCLUSIONS

The first two years of life are a critical period, during which several factors can increase the risk of FA development in genetically predisposed children.

Pharmacological and Nutritional Modulation of Metabolome and Metagenome in Cardiometabolic Disorders

Cardiometabolic disorders are major causes of morbidity and mortality worldwide. A growing body of research indicates that the gut microbiota, whether it interacts favorably or not, plays an important role in host metabolism. Elucidating metabolic pathways may be crucial in preventing and treating cardiometabolic diseases, and omics methods are key to studying the interaction between the fecal microbiota and host metabolism. This review summarizes available studies that combine metabolomic and metagenomic approaches to describe the effects of drugs, diet, nutrients, and specific foods on cardiometabolic health and to identify potential targets for future research.

Microbiota-accessible carbohydrates (MACs) as novel gut microbiome modulators in noncommunicable diseases

The gut microbiota has a significant role in human health and is affected by many factors. Diet and dietary components have profound impacts on the composition of the gut microbiome and largely contribute to the change in bacterial flora. A high-fiber diet increased dietary fiber (DF) fermentation and the production of short-chain fatty acids (SCFAs), which increased the number of microorganisms. Microbiota-accessible carbohydrates (MACs), a subgroup of fermentable carbohydrates such as DF, are defined as indigestible carbohydrates metabolized by microbes. These carbohydrates are important components to sustain the microbial environment of the complicated digestive tract and avoid intestinal dysbiosis. Each MAC has a unique property and can therefore be used as a sensitive output microbiota modulator to support host homeostasis and modulate health. In addition to the overall health-developing effects, MACs are thought to have a promising effect on the prevention of non-communicable diseases (NCDs), which are major health problems worldwide. The aim of the manuscript was to describe microbiota-accessible carbohydrates and summarize their effects on gut modulation and NCDs.

Gut microbiota promoting propionic acid production accompanies diet-induced intentional weight loss in cats

Rodent models and human clinical studies have shown gut microbiota-derived short-chain fatty acids (SCFAs) play roles in obesity and insulin resistance. These roles have been minimally explored in cats, where in the USA an estimated 60% of cats are overweight or obese. Overweight/obese research cats (n = 7) were transitioned from a maintenance diet to a reduced calorie diet fed ad libitum for seven days, then calories were restricted to achieve 1-2% weight loss per week for an additional 77 days. Cats then received their original maintenance diet again for 14 days. Significant intentional weight loss was noted after calorie restriction (adjusted p < 0.0001). 16S rRNA gene amplicon sequencing and targeted SCFA metabolomics were performed on fecal samples. Fecal microbial community structure significantly differed between the four study phases (PERMANOVA p = 0.011). Fecal propionic acid was significantly higher during diet-induced weight loss (adjusted p < 0.05). Spearman correlation revealed the relative abundances of Prevotella 9 copri (ρ = 0.6385, p = 0.0006) and Blautia caecimuris (ρ = 0.5269, p = 0.0068) were significantly correlated with propionic acid composition. Like humans, obese cats experienced an altered microbial community structure and function, favoring propionic acid production, during diet-induced weight loss.

Short chain fatty acids and GIT hormones mitigate gut barrier disruption in high fat diet fed rats supplemented by synbiotics

High fat diet (HFD) predisposes to many metabolic changes; it may disrupt gut barrier integrity and gut microbiota composition. Synbiotic supplementation may promote host’s metabolic health by selective activation of the healthy microorganisms. This study aimed to probe the interaction between synbiotic supplementation, gut microbiota and gut hormones in HFD states. Twenty-seven adult male albino rats, 3 groups, group I: control, group II: HFD received HFD for 12 weeks and group III: synbiotic-supplemented HFD received synbiotic in the last 6 weeks. The anthropometric measurments were measured. Liver transaminases, lipid profile, parameters of insulin resistance, serum serotonin, glucagon like polypeptide-1 (GLP-1), oxidant/antioxidant markers (MDA/GPx), zonulin levels and quantitative cecal short chain fatty acids (SCFA) were assessed. Samples of liver and colon were employed for histopathological studies. Compared to HFD group, synbiotic led to a significant reduction in anthropometric measurements, liver enzymes, atherogenic index, HOMA-IR and MDA denoting improved dyslipidemia, insulin resistance and oxidative state. Moreover, synbiotic supplementation decreased serum zonulin and increased both serum serotonin, GLP-1 and cecal SCFAs. Synbiotic supplementation ameliorated the metabolic derangements and the disturbed integrity of the intestinal barrier induced by HFD. As synbiotics can increase gut hormones (serum GLP-1&serotonin) and SCFAs.

Bile Acids and Short-Chain Fatty Acids Are Modulated after Onion and Apple Consumption in Obese Zucker Rats

Gut microorganisms are involved in the development and severity of different cardiovascular diseases, and increasing evidence has indicated that dietary fibre and polyphenols can interact with the intestinal microbiota. The study objective was to investigate the effect of onion and apple intake on the major types of microbial-derived molecules, such as short-chain fatty acids (SCFAs) and bile acids (BAs). Obese Zucker rats were randomly assigned (n = eight rats/group) to a standard diet (OC), a standard diet/10% onion (OO), or a standard diet/10% apple (OA). Lean Zucker rats fed a standard diet served as a lean control (LC) group. Faecal samples were collected at baseline, and 8 weeks later, the composition of the microbial community was measured, and BA and SCFA levels were determined using high-performance liquid chromatography-mass spectrometry (HPLC-MS) and gas chromatography-mass spectrometry (GC-MS), respectively. Rats fed onion- and apple-enriched diets had increased abundance of beneficial bacteria, such as Bifidobacterium spp. and Lactobacillus spp., enhanced SCFAs (acetic, propionic, isobutyric, and valeric acids), decreased excretion of some BAs, mainly of the primary (CA, α-MCA, and β-MCA) and secondary type (ω-MCA, HDCA, NCA, DCA, and LCA), and increased amount of taurine- and glycine-conjugated BAs compared to the OC group. The contribution of specific bioactive compounds and their metabolites in the regulation of the microbiome and the pathways linked to SCFA and BA formation and their relationship with some diseases needs further research.

Exploring the Influence of Gut Microbiome on Energy Metabolism in Humans

The gut microbiome has a profound influence on host physiology, including energy metabolism, which is the process by which energy from nutrients is transformed into other forms of energy to be used by the body. However, mechanistic evidence for how the microbiome influences energy metabolism is derived from animal models. In this narrative review, we included human studies investigating the relationship between gut microbiome and energy metabolism -i.e., energy expenditure in humans and energy harvest by the gut microbiome. Studies have found no consistent gut microbiome patterns associated with energy metabolism, and most interventions were not effective in modulating the gut microbiome to influence energy metabolism. To date, cause-and-effect relationships and mechanistic evidence on the impact of the gut microbiome on energy expenditure have not been established in humans. Future longitudinal observational studies and randomized controlled trials utilizing robust methodologies and advanced statistical analysis are needed. Such knowledge would potentially inform the design of therapeutic avenues and specific dietary recommendations to improve energy metabolism through gut microbiome modulation.

Intestinal microenvironment-mediated allergic dynamic phenotypes and endotypes in the development of gluten allergy

This study aimed to investigate the dynamic changes in intestinal microenvironment factors in the development of gluten-induced allergy (GA). Our results showed that GA provoked increasingly severe allergic phenotypes such as allergic and diarrheal symptoms with the gluten sensitization frequency, which was accompanied by dynamically rising levels of gluten-specific immunoglobulin (Ig) E, IgG2a and IgA, serum histamine, T cell-related inflammatory cytokines, and intestinal indexes. An increase in luminal pH was more significant in the large intestine versus the small intestine, which was due to a dynamic decline in colonic short-chain fatty acid levels. Both antioxidant capacity and intestinal permeability in the large intestine varied with the GA severity, as evidenced by a dynamic increase in the malondialdehyde content and a decrease in the superoxide dismutase activity and total antioxidant capacity. Moreover, we demonstrated that intestinal microenvironment dysbiosis occurred before a true allergy reaction began. Spearman correlation analysis suggested that the characteristic bacterial cluster, namely Alistipes, Desulfovibrio, Ileibacterium, Parabacteroides, and Ruminococcus torques group, are essential in the association between GA and intestinal microenvironment homeostasis.

Microbiota-gut-adipose axis: butyrate-mediated the improvement effect on inflammatory response and fatty acid oxidation dysregulation attenuates obesity in sleep-restricted mice

BACKGROUND

Insufficient sleep was considered as a substantial cause of obesity. The present study further explored the mechanism whereby sleep restriction (SR)-mediated intestinal dysbiosis induced metabolic disorder and ultimately lead to obesity in mice and the improvement effect of butyrate exerting on it.

METHODS

A continuous 3 months SR mouse model with or without butyrate supplementation and fecal microbiota transplantation to explore the key role of intestinal microbiota in butyrate improving inflammatory response in inguinal white adipose tissue (iWAT) and fatty acid oxidation dysfunction in brown adipose tissue (BAT), further ameliorating SR-induced obesity.

RESULTS

SR-mediated gut microbiota dysbiosis (down-regulation in butyrate level and up-regulation in LPS level) induced intestinal permeability increase and inflammatory response in iWAT and fatty acid oxidation dysfunction in BAT, ultimately resulting in obesity. Further, we demonstrated butyrate ameliorated gut microbiota homeostasis, suppressed inflammatory response via GPR43/LPS/TLR4/MyD88/GSK-3β/β-catenin loop in iWAT and restored fatty acid oxidation function via HDAC3/PPARα/PGC-1α/UCP1/Calpain1 pathway in BAT, ultimately reversing SR-induced obesity.

CONCLUSIONS

We revealed that gut dysbiosis is a key factor for SR-induced obesity and provided a better understanding of the effects of butyrate. We further expected that reversing SR-induced obesity by improving microbiota-gut-adipose axis disorder could be a possible treatment for metabolic diseases.

Gut microbiota short-chain fatty acids and their impact on the host thyroid function and diseases

Thyroid disorders are clinically characterized by alterations of L-3,5,3',5'-tetraiodothyronine (T4), L-3,5,3'-triiodothyronine (T3), and/or thyroid-stimulating hormone (TSH) levels in the blood. The most frequent thyroid disorders are hypothyroidism, hyperthyroidism, and hypothyroxinemia. These conditions affect cell differentiation, function, and metabolism. It has been reported that 40% of the world's population suffers from some type of thyroid disorder and that several factors increase susceptibility to these diseases. Among them are iodine intake, environmental contamination, smoking, certain drugs, and genetic factors. Recently, the intestinal microbiota, composed of more than trillions of microbes, has emerged as a critical player in human health, and dysbiosis has been linked to thyroid diseases. The intestinal microbiota can affect host physiology by producing metabolites derived from dietary fiber, such as short-chain fatty acids (SCFAs). SCFAs have local actions in the intestine and can affect the central nervous system and immune system. Modulation of SCFAs-producing bacteria has also been connected to metabolic diseases, such as obesity and diabetes. In this review, we discuss how alterations in the production of SCFAs due to dysbiosis in patients could be related to thyroid disorders. The studies reviewed here may be of significant interest to endocrinology researchers and medical practitioners.

Characteristics of the gut microbiota in bipolar depressive disorder patients with distinct weight

BACKGROUND

Preliminary studies have indicated metabolic dysfunction and gut dysbiosis in patients with bipolar disorder (BD). In this study, we aimed to clarify the impact of the gut microbial composition and function on metabolic dysfunction in BD patients with an acute depressive episode.

METHODS

Fresh fecal samples were provided from 58 patients with BD depression, including 29 with normal weight (NW) and 29 with overweight/obesity (OW), and 31 healthy controls (HCs). The hypervariable region of 16 S rRNA gene (V3-V4) sequencing was performed using IonS5TMXL platform to evaluate the bacterial communities. Differences of microbial community and correlation to clinical parameters across different groups were analyzed.

RESULTS

Compared to NW and HCs, the OW group showed a decreased tendency in alpha diversity index. Beta diversity was markedly different among these groups (PERMANOVA: R2  = 0.034, p = 0.01) and was higher in patients versus HCs. A total number of 24 taxa displayed significantly different abundance among OW, NW, and HCs. At the family level, the abundance of three taxa was remarkably increased in NW, one in OW, and one in HCs. At the genus level, five taxa were enriched in OW, eight in NW, and two in HCs. The relative abundance of the genera Megamonas was positively associated with BMI, while Eggerthella was negatively correlated with BMI. Functional prediction analysis revealed the metabolism of cofactors and vitamins and amino acid were highly enriched in OW compared to HCs. In addition, microbial functions involved in "lipid metabolism" were depleted while the "fructose and mannose metabolism" was enriched in OW compared to NW group.

CONCLUSIONS

Specific bacterial taxa involved in pathways regulating the lipid, energy, and amino acid metabolisms may underlie the weight concerns in depressed BD patients. Potential targeting gut microbial therapy is provided for overweight/obesity patients with BD, which still need further studies in the future.

Can prebiotics help tackle the childhood obesity epidemic?

Globally, excess weight during childhood and adolescence has become a public health crisis with limited treatment options. Emerging evidence suggesting the involvement of gut microbial dysbiosis in obesity instills hope that targeting the gut microbiota could help prevent or treat obesity. In pre-clinical models and adults, prebiotic consumption has been shown to reduce adiposity partially via restoring symbiosis. However, there is a dearth of clinical research into its potential metabolic benefits in the pediatric population. Here, we provide a succinct overview of the common characteristics of the gut microbiota in childhood obesity and mechanisms of action of prebiotics conferring metabolic benefits. We then summarize available clinical trials in children with overweight or obesity investigating the effects of prebiotics on weight management. This review highlights several controversial aspects in the microbiota-dependent mechanisms by which prebiotics are thought to affect host metabolism that warrant future investigation in order to design efficacious interventions for pediatric obesity.

Short-Chain Fatty Acids-A Product of the Microbiome and Its Participation in Two-Way Communication on the Microbiome-Host Mammal Line

PURPOSE OF REVIEW

The review aims to describe short-chain fatty acids (SCFAs) as metabolites of bacteria, their complex influence on whole-body metabolism, and alterations in the SCFA profile in obesity and after bariatric surgery (BS).

RECENT FINDINGS

The fecal profile of SCFAs in obese patients differs from that of lean patients, as well as their gut microbiota composition. In obese patients, a lower diversity of bacteria is observed, as well as higher concentrations of SCFAs in stool samples. Obesity is now considered a global epidemic and bariatric surgery (BS) is an effective treatment for severe obesity. BS affects the structure and functioning of the digestive system, and also alters gut microbiota and the concentration of fecal SCFAs. Generally, after BS, SCFA levels are lower but levels of branched short-chain fatty acids (BSCFAs) are elevated, the effect of which is not fully understood. Moreover, changes in the profile of circulating SCFAs are little known and this is an area for further research. Obesity seems to be inherently associated with changes in the SCFA profile. It is necessary to better understand the impact of BS on microbiota and the metabolome in both feces and blood as only a small percentage of SCFAs are excreted. Further research may allow the development of a personalized therapeutic approach to the BS patient in terms of diet and prebiotic intervention.

Short-Chain Fatty-Acid-Producing Bacteria: Key Components of the Human Gut Microbiota

Short-chain fatty acids (SCFAs) play a key role in health and disease, as they regulate gut homeostasis and their deficiency is involved in the pathogenesis of several disorders, including inflammatory bowel diseases, colorectal cancer, and cardiometabolic disorders. SCFAs are metabolites of specific bacterial taxa of the human gut microbiota, and their production is influenced by specific foods or food supplements, mainly prebiotics, by the direct fostering of these taxa. This Review provides an overview of SCFAs' roles and functions, and of SCFA-producing bacteria, from their microbiological characteristics and taxonomy to the biochemical process that lead to the release of SCFAs. Moreover, we will describe the potential therapeutic approaches to boost the levels of SCFAs in the human gut and treat different related diseases.

Obesogenic diet leads to luminal overproduction of the complex IV inhibitor H2 S and mitochondrial dysfunction in mouse colonocytes

Obesity is characterized by systemic low-grade inflammation associated with disturbances of intestinal homeostasis and microbiota dysbiosis. Mitochondrial metabolism sustains epithelial homeostasis by providing energy to colonic epithelial cells (CEC) but can be altered by dietary modulations of the luminal environment. Our study aimed at evaluating whether the consumption of an obesogenic diet alters the mitochondrial function of CEC in mice. Mice were fed for 22 weeks with a 58% kcal fat diet (diet-induced obesity [DIO] group) or a 10% kcal fat diet (control diet, CTRL). Colonic crypts were isolated to assess mitochondrial function while colonic content was collected to characterize microbiota and metabolites. DIO mice developed obesity, intestinal hyperpermeability, and increased endotoxemia. Analysis of isolated colonic crypt bioenergetics revealed a mitochondrial dysfunction marked by decreased basal and maximal respirations and lower respiration linked to ATP production in DIO mice. Yet, CEC gene expression of mitochondrial respiration chain complexes and mitochondrial dynamics were not altered in DIO mice. In parallel, DIO mice displayed increased colonic bile acid concentrations, associated with higher abundance of Desulfovibrionaceae. Sulfide concentration was markedly increased in the colon content of DIO mice. Hence, chronic treatment of CTRL mouse colon organoids with sodium sulfide provoked mitochondrial dysfunction similar to that observed in vivo in DIO mice while acute exposure of isolated mitochondria from CEC of CTRL mice to sodium sulfide diminished complex IV activity. Our study provides new insights into colon mitochondrial dysfunction in obesity by revealing that increased sulfide production by DIO-induced dysbiosis impairs complex IV activity in mouse CEC.

Associations between fecal short-chain fatty acids, plasma inflammatory cytokines, and dietary markers with depression and anxiety: Post hoc analysis of the ENGAGE-2 pilot trial

BACKGROUND

The microbiome-gut-brain-axis (MGBA) is emerging as an important mechanistic link between diet and mental health. The role of significant modifiers of the MGBA, including gut microbial metabolites and systemic inflammation, in individuals comorbid with obesity and mental disorders, is under-investigated.

OBJECTIVES

This exploratory analysis examined associations among microbial metabolites-fecal SCFAs, plasma inflammatory cytokines, and diet with depression and anxiety scores in adults comorbid with obesity and depression.

METHODS

Stool and blood were obtained from a subsample (n = 34) of participants enrolled in an integrated behavioral intervention for weight loss and depression. Pearson partial correlation and multivariate analyses determined associations among changes in fecal SCFAs (propionic, butyric, acetic, and isovaleric acids), plasma cytokines [C-reactive protein, interleukin 1 beta, interleukin 1 receptor antagonist (IL-1RA), interleukin 6, and TNF-α], and 35 dietary markers over 2 mo, and changes in SCL-20 (Depression Symptom Checklist 20-item) and GAD-7 (Generalized Anxiety Disorder 7-Item) scores over 6 mo.

RESULTS

Changes in the SCFAs and TNF-α at 2 mo were positively associated (standardized coefficients: 0.06-0.40; 0.03-0.34) with changes in depression and anxiety scores at 6 mo, whereas changes in IL-1RA at 2 mo were inversely associated (standardized coefficients: -0.24; -0.05). After 2 mo, changes in 12 dietary markers, including animal protein, were associated with changes in SCFAs, TNF-α, or IL-1RA at 2 mo (standardized coefficients: -0.27 to 0.20). Changes in 11 dietary markers, including animal protein, at 2 mo were associated with changes in depression or anxiety symptom scores at 6 mo (standardized coefficients: -0.24 to 0.20; -0.16 to 0.15).

CONCLUSIONS

Gut microbial metabolites and systemic inflammation may be biomarkers of importance within the MGBA, linking dietary markers, such as animal protein intake, to depression and anxiety for individuals with comorbid obesity. These findings are exploratory and warrant replication.